It is frequently necessary to position a patient in relation to medical devices. For example, in medical imaging methods, such as X-ray, a patient located on a recumbent board (cantilevered support means or member) is frequency displaced relative to a scan region of a diagnostic apparatus during examination. In many cases, the recumbent board is supported only at one end to allow access to a patient lying on the board. Therefore, it inevitably bends with increasing forward displacement of the recumbent board or with a heavy patient resting on the recumbent board. The deflection cannot be completely avoided even with a recumbent board that is designed to minimize instability.
For large patients the current designs of beds are extremely rigid and subsequently large. Additional support at the rear end of a cantilevered support member for a patient is required to counter act further deflection of the cantilever. This limits the deflection at the worst case situation to a known minimum that is an acceptable value. The position of the bed can be compensated if the deflection is known. The deflection could be measured by using strain sensors attached to the bed. However, the material of the sensors and wires would cause artifacts in the calculation of deflection. Determining the compensation by estimating the deflection based on the weight of a patient is insufficient because the distribution of the weight of the patient is not uniform.
In a more specific example of background art, such as radiation therapy systems, the patient is placed horizontally on a patient tabletop, and then positioned laterally and vertically such that a diseased region to be irradiated comes to be located precisely in the iso-center (the intersection of the horizontal and vertical axes at the treatment center). To enable performing this positioning exactly, the patient is as a rule marked beforehand in a simulator, and/or the tumor is located exactly beforehand using an imaging device. To achieve adequate positioning of the diseased tissue in the iso-center, the 3-D data obtained for instance in a computed tomography are also transmitted to the radiation therapy system, where they are used for patient positioning, or else the patient is oriented on the therapy system by means of markings made on the patient—for instance, using what is known as a “laser cross” (i.e., a projected cross-hair or target). The patient tabletop is supported by a lifting column disposed eccentrically to the iso-center. For reasons of structural height, among others, a load-bearing element that supports the patient tabletop and is supported rotatably about the vertical iso-axis is as a rule mounted at least in part in a well or a tub in the floor. Radiation therapy systems or patient support devices of the above type have been described for instance in U.S. Pat. No. 4,885,998. The problem in these systems is that the relative positioning of the patient and the medical device is made inaccurate by the deflection caused by the weight of the patient on the patient tabletop.
Additionally, a deflection of a bed is not uniform, because the weight distribution of a patient is not uniform. For example, the area of the bed supporting the head of a patient would deflect less compared with the area of the bed supporting the torso of a patient. Consequently, the deflection of the bed is not accurately assessed when only considering a point on the cantilevered bed.
In view of the prior art discussed above, there is a need to provide a device and method allowing for a more precise calculation and assessment of the deflection of a support member for patients than the conventional prior art. This would allow a more accurate positioning of patients on the support member in relation to medical devices. Further, good spatial information of the relevant part of the patient can be assessed. Hereby patients can be treated in a more target-specific manner resulting in, for example, reduced radiation dosage when X-rayed.
There also exists a need to minimize the structure of the support member and avoid a rear end support for the cantilever. The construction of the support member should be simple from a technical and an economical perspective.
Additionally, it is desirable to avoid cumbersome arrangements that would interfere with the field of view around the support member of the patient.